The present disclosure relates generally to radio frequency receivers. More particularly, the present disclosure relates to mitigating the effects of intermodulation distortion in a radio frequency receiver, such as a wideband receiver.
The use of wideband signals has increased considerably in recent years across a number of different industries. For example, wideband signals are often employed in communication systems to support higher data rates since wideband signals afford greater bandwidths over that of narrowband signals. Communication technologies such as spread spectrum techniques also utilize wideband signals to accomplish secure communications. In another example, wideband signals may be used in radar systems to afford greater degrees of precision over narrowband radar systems.
One troublesome source of distortion in a wideband system is intermodulation distortion. Ever-present and inescapable non-linearities in a wideband system may cause the generation of additional spurious signals. These non-linearities, while generally small, may exist even in the so-called linear range of an amplifier and well below the saturation point of the amplifier. Typically, a single signal at an off-channel frequency can be filtered out at the intermediate frequency and will not “spill over” on-channel, so long as the signal level does not exceed the saturation point of the circuitry of the system. In some cases, however, two or more signals at off-channel frequencies can generate a third frequency, a spurious signal that falls on-channel, resulting in intermodulation distortion.
Intermodulation distortion is particularly detrimental in wideband systems over that of narrowband systems. First, nearly all wideband systems utilize only a small number of channel assignments. Multiple off-channel signals generating intermodulation distortion are likely to produce a signal that falls on a desired channel used by the system. Second, many long distance wideband receivers utilize high gain amplifiers in their front ends to achieve the very low noise figures needed for link closure. Consequently, such receivers may go into compression at low input levels leading to intermodulation distortion generation at low input signal levels. Accordingly, applicant has discovered that there may be a need for systems and methods that mitigate intermodulation distortion in a radio receiver, such as a wideband receiver.